Production of strip from powdered metal

ABSTRACT

A process is provided for rolling metal strip particularly iron or iron alloy strip, directly from powdered metal using a technique in which a self-supporting metal powder/binder strip is formed on a support surface from a slurry containing the metal and binder composition, the support surface being precoated with a release agent. Typical release agents are mono-basic fatty acids, such as steric and oleic acids.

United States Patent Davies et al.

[ 51 Apr. 25, 1972 PRODUCTION OF STRIP FROM POWDERED METAL Inventors:ldwal Davies, Killay, Swansea; Thomas Arthur Canning, Newton, Swansea;Alan G. Harris, Tycoch, Swansea, all of Wales Assignee: The British Ironand Steel Research Association, London, England Filed: July 1, 1969Appl. No.: 838,325

Foreign Application Priority Data July 10, 1968 Great Britain..32,957/68 U.S. Cl ..75/200, 75/214 Int. Cl. ..B22f 1/00 Field ofSearch ..75/200, 214; 156/289; 264/213 Primary ExaminerCarl D. QuarforthAssistant Examiner-R. L. Tate Attorney-Sughrue, Rothwell, Mion, Zinn &Macpeak [5 7] ABSTRACT A process is provided for rolling metal stripparticularly iron or iron alloy strip, directly from powdered metalusing a technique in which a self-supporting metal powder/binder stripis formed on a support surface from a slurry containing the metal andbinder composition, the support surface being precoated with a releaseagent. Typical release agents are mono-basic fatty acids, such as stericand oleic acids.

11 Claims, No Drawings PRODUCTION OF STRIP FROM POWDERED METAL CROSSREFERENCES TO RELATED APPLICATIONS U.S. Application 683,983, filed 17thNov. 1967. U.S. Application 807,ll,filed 13th Mar. 1969.

BACKGROUND OF THE INVENTION This invention relates to a process for theproduction of metal strip from powdered metal which is particularly, butnot exclusively, applicable to the production of steel strip.

In our co-pending application Ser. No. 683,983 filed 17th Nov. 1967there is described a process for the production of strip from powderedmetal which comprises depositing a layer of powdered metal onto asupport surface, removing the layer from the support surface and thenrolling the layer to effect compaction and sintering the compacted layerat a temperature below the melting poing of the metal. In accordancewith one embodiment of the process described in our abovementionedapplication, the powdered metal is initially deposited onto the supportsurface as a coating in the form of a slurry comprising a suspension ofmetal powder in a binder composition, one example of a suitable bindercomposition being an aqueous methyl cellulose solution.

After drying, the resulting metal powder binder strip is removed fromthe substrate and then subjected to rolling to effect compaction of thepowdered metal and the compacted strip is then sintered. Provided thatthe slurry formed from the binder and the powdered metal is sufficientlyviscous, little difficulty is normally experienced in cleanly strippingthe dried film from a smooth substrate, such as a stainless steel band.It is, however, desirable in order to increase the line speed of theprocess to reduce the viscosity of the slurry to the minimum consistentwith maintaining good metal powder/binder strip formation and adequatesuspension of the powdered metal. It is found, however, that reductionof the viscosity of the slurry below about 50,000 centipoises tends togive a more brittle and less easily handled metal powder/binder stripwhich is more difficult to remove cleanly from the substrate as a resultof a tendency to adhere to the substrate. While we have found that theaddition of a hygroscopic substance, e.g., glycerol, to the suspensionplasticises the resultant dried film and results in a strip whichexhibits increased flexibility and cohesion, the dried strip may stillexhibit a tendency to adhere to the substrate. The addition ofhygroscopic substances to metal powder/binder slurries is the subject ofour co-pending application Ser. No. 807,101 filed 13th Man, 1969 whichalso refers to the beneficial effect of the hygroscopic substance inimproving the physical properties of the final metal strip.

Preferably, the hygroscopic substance is a water-soluble polyhydroxycompound, such as glycerol, low moleculor weight polyalkylene glycols,e.g., trimethylene glycol, polyhydric alcohols, e.g., sorbitol,mannitol, and sugars, e.g., invert sugar. Inorganic hydroscopicmaterials may also be employed, such as calcium chloride. Thehydroscopic substance is preferably present in an amount up to 1.0percent by weight of the suspension employed. It has been noted that ifa substantially larger portion of the hydroscopic substance is employed,too much water tends to be retained in the cellulose derivative duringthe slurry drying which leads to difficulties in the subsequentprocessing steps.

SUMMARY OF THE INVENTION The present application is concerned with asolution to the problem of undesirable adhesion to the substrate ofdried films formed from powdered metal/binder compositions. We have nowdiscovered, that this difficulty can be overcome by coating thesubstrate with a thin film of a release agent prior to the deposition ofthe slurry of powdered metal and binder composition.

Examples of suitable release agents are fatty acids, e.g., mono-basicacids such as oleic and stearic acids fluorinated hydrocarbons,particularly fluorinated hydrocarbon polymers,

e.g., polytetrafluoroethylene and silicones. In the case of fluorinatedhydrocarbons and silicones a permanent release film is obtained on thesupport surface, the films being applied by methods known in the art.

The release agent is desirably coated in a thin film onto the supportsurface and in the case of mono-basic fatty acid, this may be achieveddirectly (i.e. alone without the agency of a solvent or dispersant) orin the form of a solution or dispersion with subsequent removal of thecontinuous phase of the solution or dispersion. Convenient solvents forfatty acids are, for example, trichloroethylene or ethanol. The solutionor dispersion (when used) may be applied to the support surface by anyconvenient method, such as roller coating, spraying or using a rotatinglambswool coated roller impregnated with the solution. The continuousphase may be evaporated or allowed to evaporate before the suspension ofpowdered metal and binder composition is applied to the support surface.

It has been found that a 1 percent solution of a mono-basic fatty acid,such as oleic or stearic acid, in trichloroethylene or ethanol isextremely satisfactory, (although other concentrations may be used). Byrotating the application roller in contact with the substrate, a verythin film of oleic acid or stearic acid can be applied to the surfaceand this ensures that the deposited, dried metal powder/binder stripfilm can be readily removed from the substrate. Preferably the fattyacid is applied continuously to the support surface. Generally where theslurry is coated continuously onto an endless belt or drum, as describedin our co-pending application Ser. No. 683,983 the fatty acid isconveniently applied continuously to the belt or drum at a pointupstream of the slurry coating station.

Apart from the use of the release agent the process of the presentinvention is carried out in the manner described in our co-pendingpatent application Ser. No. 683,983.

What we claim is:

1. A process for the production of a strip from powdered metal whichcomprises:

a. Forming on a support surface a thin film of a release agent;

b. Depositing on said film a coating of slurry comprising a suspensionof powdered metal in an aqueous solution of a film-forming cellulosederivative, said slurry having a viscosity of less than 50,000centipoises;

c. Drying said coating on said support surface;

d. Removing the resultant dried coating from the support surface;

e. Rolling the dried coating to effect compaction; and

f. Sintering the compacted coating at a temperature below the meltingpoint of the metal.

2. A process according to claim 1 in which the cellulose derivative is acellulose ether containing methyl groups.

3. A process according to claim 1 in which the release agent is a fattyacid.

4. A process according to claim 4 in which the fatty acid is oleic orstearic acid.

5. A process according to claim 1 in which the support surface is a drumor an endless metal belt onto which the slurry is continuously coatedand from which the dried coating is continuously removed.

6. A process according to claim 5 in which the release agent is a fattyacid and is coated continuously onto the belt or drum at a pointupstream of a slurry coating station.

7. A process according to claim 1 in which the release agent is afluorinated hydrocarbon or a silicone.

8. A process according to claim I in which the release agent is a fattyacid and is deposited on the support surface from a solution ordispersion.

9. A process according to claim 1 in which the slurry includes ahygroscopic substance selected from the group consisting of, lowmolecular weight polyalkylene glycols, polyhydric alcohols, sugars, andcalcium chloride.

10. A process according to claim 9 wherein said polyhydric alcohol isglycerol.

11. A process for the production of a strip from powdered metal whichcomprises:

d. Removing the resultant dried coating from the support surface;

e. Rolling the dried coating to effect compaction; and

f. Sintering the compacted coating at a temperature below the meltingpoint of the metal.

2. A process according to claim 1 in which the cellulose derIvative is acellulose ether containing methyl groups.
 3. A process according toclaim 1 in which the release agent is a fatty acid.
 4. A processaccording to claim 4 in which the fatty acid is oleic or stearic acid.5. A process according to claim 1 in which the support surface is a drumor an endless metal belt onto which the slurry is continuously coatedand from which the dried coating is continuously removed.
 6. A processaccording to claim 5 in which the release agent is a fatty acid and iscoated continuously onto the belt or drum at a point upstream of aslurry coating station.
 7. A process according to claim 1 in which therelease agent is a fluorinated hydrocarbon or a silicone.
 8. A processaccording to claim 1 in which the release agent is a fatty acid and isdeposited on the support surface from a solution or dispersion.
 9. Aprocess according to claim 1 in which the slurry includes a hygroscopicsubstance selected from the group consisting of, low molecular weightpolyalkylene glycols, polyhydric alcohols, sugars, and calcium chloride.10. A process according to claim 9 wherein said polyhydric alcohol isglycerol.
 11. A process for the production of a strip from powderedmetal which comprises: a. Forming on a support surface a thin film of afatty acid release agent; b. Depositing on said film a coating of slurrycomprising a suspension of powdered metal in an aqueous solution of afilm-forming cellulose derivative, said slurry having a viscosity ofless than 50,000 centipoises; c. Drying said coating on said supportsurface; d. Removing the resultant dried coating from the supportsurface; e. Rolling the dried coating to effect compaction; and f.Sintering the compacted coating at a temperature below the melting pointof the metal.